<p>Metal-organic frameworks (MOFs), that have emerged as promising electrocatalysts in oxygen evolution reaction (OER), usually undergo structural reconstruction to form metal hydroxides as active sites. However, it remains a great challenge to design and synthesize ideal MOF-based pre-catalysts for properly cognizing and utilizing the reconstruction process toward efficient OER activity. Herein, the well-defined MOF-808 is post-modified by 2-hydroxyphosphonoacetic acid (HPAA) to form a micro-adsorber that enables to capture of metal ions effectively. Fe³⁺ and Ni²⁺ ions are synergistically anchored into the micro-adsorber, developing a Fe/Ni-containing pre-catalyst that can be dynamically electrooxidized to be an active and stable dual-site electrocatalyst denoted by R-MOF-HPAA@FeNi with abundant metal sites. As a result, R-MOF-HPAA@FeNi exhibits an excellent OER performance with a low overpotential of 272 mV and Tafel slope of 35.9 mV dec⁻¹, as well as long-term stability over 300 hat 10 mA cm⁻². Experiments and theoretical calculations suggest the resulting catalyst mainly follows a lattice oxygen mechanism (LOM) of dual-metal-site mechanism (DMSM). Owing to the chelating role of HPAA, the post-synthesized MOF-HPAA behaves as a trap to uniformly and firmly adhere Fe³⁺ and Ni²⁺ ions, leading to a functionalized MOF-based pre-catalyst which can be structurally evolved into atomic level-distributed OER electrocatalysts.</p>